Isostatic pressing of objects by the wet bag system involves the placing of a pre-formed object in an elastomeric bag which is then placed in the cavity of a press and the press is closed. Hydraulic fluid then is admitted to the press wetting the outside surface of the bag and as the pressure is increased the bag yields to conform to the shape of the object whereby the pressure is isostatically exerted upon the object to form it into a compact. After pressing and lowering of pressure on the hydraulic fluid the bag is removed for extraction of the compact and reloading of the bag with another pre-formed shape. This entire operation is inherently slow and involves a great amount of manual handling of the bags, pre-formed shapes and the compacts.
In contrast with this, as illustrated in U.S. Pat. Nos. 3,557,405 and 3,591,903 for example, the isostatic forming and pressing of objects directly from powder have been effectively automated being performed in multi-cavity presses or in single cavity presses with mechanical auxiliaries for loading the cavity or cavities with powder and extracting the pressed compacts in cyclic fashion. In devices of the latter type the cavity or cavities consist of hollow molds of specific shape for the formation of a compact having that shape when pressing is completed. Thus, in operation, the mold cavities are opened, a measured amount of powder is poured into the cavity and, after closure of the vessel, the pressing step is performed. The compact thus formed is removed by manual or automatic means either through the same opening used for filling or through an oppositely disposed opening as may be preferred or required.
In devices of the latter type the molds are formed of one or more bodies of elastomeric material having hollows therein of the specific shape required. Thus, the production is limited to that specific shape and size of compact unless a new mold or set of molds is substituted. Also, there are limitations on the types of shapes that may be formed and compacted in such devices without involving considerable complication such as making the molds in several pieces.
In this background there is need for a method useful with apparatus having the relatively great versatility of the wet bag presses to provide convenient manual and, if desired automated, loading and unloading of pre-formed shapes.